Field of the Invention
This invention relates generally to a photosensitive transducer and, more particularly, to an improved photosensitive transducer which is characterized by a high degree of light transmissivity therethrough, together with a highly desirable range of photoconductive and photovoltaic sensitivities.
2. Description of the Prior Art
Photosensitive tranducers are well known in the art and many exhibit photoconductive and/or photovoltaic properties. The term photoconductive generally means that the transducer is subject to a change in resistance impedance when subjected to radiation such as visible light. The term photovoltaic generally means that the transducer displays a varying output potential as a function of the radiation to which it is exposed.
Such photosensitive transducers have found general use in automatic exposure control systems for photographic apparatus. Exposure control systems basically function to evaluate scene brightness or illumination and weight this evaluation with respect to the sensitometric characteristics of the film being exposed so as to regulate one or more variable exposure control parameters, as for instance, exposure interval or aperture size in correspondence with the weight of the evaluation. Scene brightness evaluation may be performed by light measuring circuits utilizing one or more photosensitive transducers positioned upon a camera apparatus. The transducers are aligned in a manner to be responsive to the light characteristics of a scene approximately coincidence with that of the field of view of the camera lens system. Such photosensitive transducers may even be made substantially transparent and thus stationed in overlapping relation with respect to the camera lens system in order to evaluate a scene directly coincident with that of the field of view of the camera lens. The scene evaluated in this manner will have the exact light characteristics as the scene viewed by the camera lens.
Photosensitive transducers of a type suitable for use in the above-described exposure control system may also experience performance limitations. The output signal response of such photosensitive transducers is often insufficient to provide an adequate evaluation of the various levels of scene brightness which might normally be encountered, as for instance, between photographing indoors vs. outdoors. Such insufficiencies are due normally to the non-linear performance displayed by the transducer over the brightness region of interest for ordinary photographic purposes.
Photosensitive transducers of the above-described type having a high degree of radiation transmissivity there-through have also been proposed for use as solar cells on satellites or other similar objects due to their substantially equal response to solar radiation received from either of two opposite directions. In this manner, the number of solar cells may be reduced by one-half the number of solar cells otherwise required. Such cells have been described as substantially translucent and embody thin conductive films of such materials as copper oxide or tin oxide. Photosensitive transducers of this type, although sufficiently translucent to be equally responsive to radiation received from either of two opposite directions, are not polarized. Thus, the determination of positive and negative terminals when utilizing such a photosensitive transducer in the photovoltaic mode becomes dependent on the actual orientation of the cell with respect to the direction of light impingment.
Therefore, it is an object of this invention to provide a polarized, substantially transparent, photosensitive transducer having a highly desirable linear range of photovoltaic sensitivities.
It is a further object of this invention to provide a polarized, substantially transparent, photosensitive transducer which exhibits a highly desirable linear range of photoconductive sensitivities in approximately inverse relation with the log of intensity of illuminance to which the transducer is exposed.
It is an even further object of this invention to provide a polarized photosensitive transducer having a high degree of light transmissivity therethrough which transducer may be constructed in a simple and economical manner utilizing conventional sputtering apparatus.